With the development of communications network technologies, changing of a network to which a terminal belongs or changing of a location of the terminal often causes the terminal to be unable to use a current transmission mode for sending data. For example, in a wireless communication network, a device to device (D2D) device performs cellular communications with a base station and sends data through communications resources allocated by the base station, which is the same as a normal terminal device. Actually, the D2D device may be at different positions in a cell of the base station (center or edge of the cell) due to moving of a holder of the D2D device, and sometimes even moves to an area out of wireless network coverage (e.g. a basement). When the D2D device is at the center of the cell, a transmission mode which is to send data using a communications resource allocated by the base station can be used. However, when the D2D device moves to the edge of the cell or an area out of network coverage, since signal power is poor or even there's no wireless signal, the terminal cannot use the transmission mode of sending data by using the communications resource allocated by the base station, i.e. the current transmission mode cannot be used, thus resulting in communications interruption. Therefore, there is no conversion of transmission mode in the prior art, which is unpractical and cannot achieve a conversion to other transmission modes for sending data when the current transmission mode cannot be used.